Cathode ray intensity control circuit



J. J. MAHONEY, JR

Filed F'eb. 24, 1943 CATHODE RAY INTENSITY CONTRL CIRCUIT.l

March i4, 1944.

ATTORNEY UNITED STATES PATENT VOFFICE- ca'rnons nar maNsrry connor.

' cmcorr John J. Mahoney, Jr., Lynbrook, N. Y., assigner to Beil Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 24, 1943, serial No. 476,945

' 4 'I'.Cl. 315-30) 12 Claims.

This invention relates to cathode-ray oscilloscope circuits vand more particularly to beam Fig. 3 illustrates a modication of the beam release coupling circuits of Figs. 1 and 2.

intensity control and metering circuits therefor` to extinguish it entirely until the instant the.

oscillogram is to start. At the instant'the sweep is initiated the beam is automatically turned on to form the oscillogram. In making photographic oscillograms with cathode ray oscilla-- scopes ln which the beam is extinguished until the sweep is initiated it isof considerable importance to know what the intensity of the beam will be before making the exposure. The circuits of this invention provides by direct reading on a meter a predetermined indication of what the beam intensity will be.

It is the object of this invention to provide a beam-intensity control and metering circuit for a cathode ray oscilloscope incorporating an easily operated intensity control for predetermining the intensity of the beam.

` Theloregoing object is achieved by this invention by providing for a cathode ray oscillo scope system of the type employing a cathode and a beam intensity modulating grid, the combination of two sources of direct current voltage one ot which provides the `normal extinction bias for its cathode ray beam while the other source of voltage provides a measured amount of voltage bias for producinga predetermined beam intensity during the time the cathode rayoscilloscope is active, and a meter adapted to indicate the dlii'erence inv voltage between said two voltage sources as ameasure of the intensity of the beam.

The invention may be better understood by referring to the accompanying drawing in which: v

Fig. 1 illustrates .an osclllograph circuit em- R'eferring vnow more particularlyV to Fig. l

th cathode ray osclllograph tube I is disclosed in connection with a'preferred form of beam deector circuit. This beam deector circuit is more particularly described in connection with applicants copending application, Serial No. 476,944, led on even date herewith. However, Y

for the purposes of this invention the operation of this portion of the circuit will be briefly described.

Cathode ray oscilloscope I has vertical and' horizontal beam deector plates 2, 2 and 3, 3, respective1y. A sweep circuit for the horizontal beam defiector plate comprises sweep condensers 8 and I0 connected in a series circuit with power source I through resistors I6, 1, 9 vand I1. Prior to initiating the sweep power source I5 charges bodying a preferred form of beam control circuit in accordance with this invention:

Fig. 2 illustrates a modliied embodiment of the beam control circuitof this invention; and

condensers 8A and III to the voltage of the power source through the series resistor circuit lust described. It will be noted that the sweep deiiector condensers 8 and Ill are connected in a balanced to ground circuit arrangement by reason of grounded conductor 3B and the grounded mid tap 2li in the power source I5. Coupling condensers II and I2 couple the horizontal plates of the oscilloscope to the sweep condensers l and IIJ. A gas-filled tube 6 is connected with its anode and cathode to-conductors I3 and I4 in the charging circuit. To initiate the sweep a synchronizing pulse is received from circuit 52 through coupling condenser 49 causing the gas-nlled tube 8 to discharge. This places a substantial short between conductors I3 and Il thereby causing sweep condensers 8 and I0 to discharge .through series-connected resistors 'I and 9. The resulting charge in voltage on sweep condensers 2 and III produces a sweep voltage for the horizontal plates 3, 3 ofthe oscilloscope I. The synchronizing pulse is customarily associated in some way electrically with the source to be observed which is received over a 'circuit 2l, ampliiled by ampliiler- 29 and transmitted to the. vertical deiector plates 2, 2 over circuit $0 and conductors 32 and .33. AThe simultaneous transmission of the phenomenon to the vertical plates and the initiation of the sweep produces the oscillogram on the oscilloscope screen in a manner well known to the art.

The sweep circuit just described has a self-contained sweep velocity timing circuit comprising a single series resonant circuit tuned to a suitare lalso charged from source I 5 through resistors I6 and i1. Upon the discharge of gas-nlled tube 6,' an oscillatory discharge takes place through this series resonant circuit producing a timing voltage across resistors 42. 42. In order to use this circuit for calibrating the velocity of the sweep, switch 3| is moved to its downward posiover conductor 59 through capacitor 58 to the tion thereby coupling circuit 39 to the vertical oscilloscope plates. Gas-lled tube 6 is then oper ated manually by operating switch 64 which discharges capacitor 46 through resistor thereby applying a positive pulse through coupling condenser 49 to the grid ofgas-lled tube 5. Condenser 46Y was .previously charged through the normally closed contacts ci switch 44 and conductor 45 from power source I5. l It will be understood that upon the operation of switch 44 and the discharge of gas-filled tube 6 the oscillatory discharge of the timing circuit including inductors 40, 40 and capacitors 4I, 4I as previousl'y described takes place.

To protect the oscilloscope screen it is essential that the cathode ray be suppressed to extinction until the sweep is initiated. Also if the beam is not suppressed the photosensitive lm will be fogged, a distracting spot will remain on the screen prior to the sweep and a confusing return trace will appear on the screen. Beam' extinction is accomplished in accordance with this invention by applying a normal bias to control grid 5 of the oscilloscope tube I from a voltage drop derived from resistor 60 associated with direct` current power source 63. The entire beam control circuit is represented generally by reference numeral 53 which comprises two direct current powersources 55p and 63. In circuit with source 55 are series-connected resistors 66 and 61 which are preferably of equal resistance, a vacuum tube triode 54|and an adjustable cathode resistor 56. Resistor 66 is by-passed with a capacitor 68. The grid of tube 54 is coupled to thelower end of cathoderesistor 56 by means of resistor 51. It is Well known that the space current through tube 54 may be adjusted over a wide range by adjusting cathode resistor 56. In circuit with direct current power source 63 is a resistancenetwork comprising resistors 60, 6I and 52. Resistors 60 and 62 are kept equal and are both adjustable through a gang adjustment as schematically indicated in the drawing. Consequently, the voltage drop across resistor 60 is always equal to the voltage drop across resistor 62. A coupling condenser 65 is connected between the grid 5 of oscilloscope I and the upper end of resistor 61 in the Ybeam control circuit. A direct current meter 54 and consequently substantially instantaneously cause the voltage drop across resistor 61 to disappear. The time constant of capacitor 1I and series-connected resistors 12 an:i y13 is sumciently long to maintain tube 54 inl a blocked condition throughout the sweep period. 4When the sweep velocity is changed by varying resistors 1 and 9 in the sweep circuit the capacity of capacitor 1I should also be changed to vary the time constant of that circuit in order to insure that the blocking pulse will be maintained throughout the sweep period. This is achieved by gauging variable capacitor 1l with the variable resistors 1 and 9 through ganging control 14.

, TheY beam control circuitV just described is operated in the following manner: With normal voltages in all of the electrodes of oscilloscope I some of which are not shown in Fig. l for the sake of clarity, the beam is biased to extinction by adjusting variable resistor 60. Having previously determined the velocity of the sweep, cathode resistor 56 is next adjusted until meter 69 indicates u sulcient difference voltage between the drop in resistor 62 and the drop in resistor 66 to produce the necessary beam intensity to form a trace on the photographic sensitive material to be employed. When a synchronizing pulse is received over circuit 52 thereby causing gas-lled tube 6 to discharge, the strong n'egative pulse previously de- Ascribed is transmitted over circuit 59 to suddenly block the ow of electrons through tube 54. This causes the ow through series resistor 61 to suddenly stop and thereby the drop across this resistor instantaneously disappears. The drop across resistor 66, however, is maintained by reason of its shunting condenser 6 8 'I'his results in a positive pulse being transmitted to the control grid 5 of oscilloscope I over capacitor 65. The time constant of resistor 65 and capacitor 68 is substantially equal to the time constant of capacitor 65 and resistor 64. This maintains the ignition pulse onbeam control grid 5 rather uniform over an appreclably longer period of time than the normal time constant of either one of the circuits.

That the indication of meter 69 will be a measure 8f the beam intensity will be evident 69, preferably of the zero center type, is connected between the upper end of the variable resistor 62 and the upper end of resistor 66 through a series resistor 10. It is evident that direct current meter 69 will indicate the difierence between the voltage drops in resistors 62 and 66.

Capacitor 1I and resistors 12 and 13 are serially connected between conductor I3 and ground in the sweep circuit. Capacitor 1I is normally charged with its upper plate positive at the same time the sweep condenser 8 is charged and upon the discharge o! gas-filled tube s this condenser discharges through resistors 12 and 13. The rewhen it is remembered that the Voltage drop across resistor 62 is always equal to the normal beam extinction voltage drop across resistor 6D and that with resistors 66 and 61 of equal resistance, the voltage drops thereacross are also equal to each other. 'Ihe grid 5 will always change in `voltage by an amount equal to the voltage drop across resistor 61 which disappears when tube 54 is suddenly blocked. If, for example, resistor 56 is adjusted so that current through tube 54 is negligiblyv small then the voltage drop across resistor 61 is likewise negligible. Meter 69 will indicate a voltage equal to the drop across resistor 66 which means that the bias on grid 5 will remain at the vbeam extinction value when,

justed until the voltage drop across resistor 66 is four volts less than the voltage drop across resistor 60. meter 69 will read four volts. means that thevoltage swing of grid 5 will be four volts short of reducing the' grid bias to This zero, or, in other words, the bias voltage will be yfour volts during the subsequent operation of the oscilloscope. It will thus be seen that meter 69 always reads the bias voltage which will exist on the beam intensity grid 6 during the exposure of the oscillograxn and can therefore be utilized for predetermining the intensity of the cathode beam.

The circuit shown in Fig. 2 is a modiiied arrangement of the beam control circuit 53 of Fig. 1 but operates in accordance with the same principle. The circuit of Fig. 2 requires power source 65 to be insulated from ground, the positive pole being below ground potential `by the voltage drop in resistor 15. This circuit, however, simpliiies the meter circuit somewhat in that the rlieostat 62 ganged with the rheostat 60 in Fig. 1 is eliminated leaving only rheostat 60. Also the voltage on the relatively small condenser 66 is greatly? reduced. In Fig. 1 this condenser normally has a potential equal to the voltage of yhigh voltage source 63, less the voltage drop in resistors 66 and 61- while in Fig. 2 the potential on this condenser is equal only to the drop across resistors 66 and 61 less the normal bias drop on resistor 60 which results in a voltage very much less than for the circuit of Fig. 1. This greatly reduces the insulation requirements forl condenser 65 and permits the use of a small condenser which is of considerable advantage in this type of circuit.

As previously stated the circuit arrangement of Fig. 2 makes unnecessary the use of a ganged rheostat 62. In this figure the normal beam cut-oftbias voltage drop across resistor 60 is compared directly with the voltage drop across resistor 66 and for this purpose meter 69 with its series resistor is connected directly between the upper end of resistor 60 and the upper end vof resistor 66. Direct current power supply 63 is accordingly reversed inpolarity with respect to resistor 66 so as to cause the upper end oi' resistor 60 to be negative with respect to its lower end. Instead of resistors 6| and 62 of Fig.

2 a single resistor 16 is connected in series withpower source 63 and resistor 60. It will be understood, of course, that the invention may be practiced by using a lower voltage source for source 63 and thereby eliminating the necessity for resistor 16. yHowever, a high voltage source such as source 63 is necessary to supply other voltages for the other electrodes in the cathode ray oscilloscope tube i and for this purpose resistor forms part of the high voltage bleederl network for these other electrodes. This same function is performed by resistor 6I in Fig. 1.

Since in Fig. 2 the power source 66 must be insulated from ground a suitable path to ground must be provided for the transient pulse transmitted to the grid circuit of tube 6l. This is furnished by capacitor 16 of relatively large capacity. It will thusv be seen that the strong negative pulse transmitted from the upper end of resistor- 12 of Fig. 1 passes over conductor 69 shown in Fig. 2 to capacitor 68, through resistor 61 and back to the grounded side of resistors 12, 13 through capacitor 16. yPower source 63 customarilyprovides by-pass condensers for its bleeder resistors. However. it may be advisable to add another capacitor 11 from the positive side of power source 66 to ground.

During the charging period of capacitor H a strong positive` pulse is transmitted over conductor 69 to the grid of tube 6l, resulting inthe now of a large space current. through' tube 66.

In Fig. 3 the transmission of this undesired positive pulse is blocked by substituting a diode Il in place of capacitor 58 of Figs. l and 2. lThe unilateral conductivity of the diode permits current transmission in only one direction..

It has been stated that it resistor 66"is made equal to resistor 61 and resistor 66 kept equal to resistor 62, meter 69 will read directly the bias voltage which will exist on grid 6 during the sweep period. 'While this is the preferred design, it' is also possible to simply keep the ratio of the resistances of 66 to '61' equal to theratio Y ycircuit therefor comprising an adjustable source of grid bias voltage connected to the cathode and to the 'modulating grid, a second voltage source, a vacuum tube repeater having a space current path, two resistors 'connected in series and` in series with the second voltage source and the space current path, a capacitor shunting one of said two resistors, space current control means for the repeater, an input circuit for the'repeater capablel of blocking the space current upon receiving a voltage pulse of predetermined magnitude a meter, a circuit connecting the meter with said bias adjusting means and. said -shunted resistor to cause the meter to 'indicate their difference voltage, and a circuit coupling -theunshunted one of said two resistors to the modulating grid whereby upon suddenly blocking the space current` said modulating grid will be brought to a less negative voltage of magnitude predetermined by the meter reading.

2. In an oscilloscope circuit of the type employing a cathode and a `beam intensity modulating grid, a beam intensity control and metering circuit therefor comprising an adjustable source of grid bias voltage connected to the cathode and to the modulating grid, asecond voltage source.- a vacuum tube repeater having a space current path, two resistors ot equal resistance connected in series and in series with the second voltage .source and the'space current path, a capacitor shunting one of said two resistors, space current control means for the repeater. an input circuit for the repeater capable ofl blocking the space current upon receiving a voltage pulse of predetermined magnitude. a meter, a circuit connecting the meter with said bias adjusting means and said shunted resistor to' cause the meter to indicate their dierence voltage, and a circuit coupling the unshunted one of said two resistors to the modulating grid whereby upon suddenly blocking the space current said modulating grid will be brought to a less negative voltagevof magnitude predetermined by the meter reading.

current path, a capacitor shunting one of said v two resistors, space current control means for the repeater, an input circuit for the repeater capable of blocking the space vcurrent upon receiving a voltage pulse of pretermined magnitude, a meter,

a circuit connecting the meter with said bias adf justing means and saidshunted resistor to cause the meter to indicate their difference voltage, and a circuit including a series-connected capacitor'coupling the unshunted one ofI said two resistors to the modulating grid whereby upon suddenly blocking the space current said modulating grid will be brought to a less negative voltage of magnitude predetermined by the meter reading.

4. In an oscilloscope circuit of the type employing a cathode and a beam intensity modulating grid, a beam intensity control and metering circuit therefor comprising an adjustable source of gridV bias voltage connected to the cathode and to the' modulating grid. a second voltage source, a vacuum tube repeater having a space current path, two resistors connected in series and in series with the second voltage source and the space current path, a capacitor shunting one of said two resistors, space current controlgrid bias voltage connected to the cathodeA and to the modulating grid, said bias voltage source comprisingtwo rheostats mechanically ganged so their resistances always remain equal, a resistorvelectrlcally connecting said two rheostats into a series circuit, a direct current voltage source connected to said series circuit; circuits connecting -said cathode and beam intensity grid to one of said rheostats whereby the grid bias voltage may be adiusted, a second voltage source, a vacuum tube repeater having a space current path, two resistors of equal resistance connected in series and in series with the second voltage source andthe space current path, a capacitor shunting one of said two resistors, space current control means for the repeater, an input circuit for the repeater capable of blocking the space current upon receiving a voltage pulse of predetermined magnitude, a meter, a circuit connecting the meter with the otherI of said rheostats and said shunted resistor to cause the meter to indicate their diil'erence voltage, and a circuit coupling the unshunted one of said two resistors to the modulating grid whereby upon suddenly blocking the space current said modulatinggrid will be brought to a less negative voltage oi' magnitude predetermined by the meter reading.

7. In an oscilloscope circuit o! the type employing a cathode and a beam intensity modulating grid, a beam intensity control and metering circuit therefor comprising an adjustable source of grid bias voltage connected to the cathode and upon suddenly blocking the space .current said modulating gridl will be brought to a less negative voltage of magnitude predetermined by the meter reading.

two rheostats into a series circuit, a direct cur-` rent voltage source connected said series circuit, circuits connecting said ca e and beam intensity grid to on'e of said rheostats whereby the grid biss ivoltage may be adjusted, a second voltage source, a'vacuum tube repeater having a space' current path, twol resistors connected in series'and in series with the second voltage source land the space current path, a capacitor shunting one of said two resistors, space current control means for the repeater, an input circuit for the repeater capable oi' blocking the space current upon receiving a lvoltage pulse of predetermined magnitude, a meter. s circuit connecting the meter with the other ci' said rheostats and said shunted resistor'to cause the meter to indicate their ditleren'ce voltage, and a circuit coupling the unshunted one of said two' resistors to the modulating mici whereby upon suddenly blocking the-space current said. modulating grid will be brought to a less negative voltage o! magnitude` predetermined by' the meter reading.

6. In an oscilloscope circuito! the type employto the modulating grid, said bias voltage source comprising two rheostats mechanically ganged together, a resistor electrically connecting said two rheostats into a series circuit. a direct current voltage source connected to said series circuit, circuits connecting said` cathode and beam intensity grid to one oi' said rheostats kwhereby the grid bias voltage may be adjusted, a second voltage source, a vacuum tube repeater having a space current path, two resistors connected in series and in series with the second voltage source and the space current path, a capacitor shunting one o! said two resistors, space current control means for the repeater, an input circuit for the repeater capable of blocking the space current upon receiving a voltage pulse of predetermined magnitude, a meter, a circuit connecting the meter with the other oi' said rheostats and said shunted resistor to cause the meter to indicate their diiierence voltage, and a circuit including a series-connected capacitor coupling the unshunted one of said two resistors to the modulating grid whereby upon suddenly ,ing a cathode and a beam intensity modulating grid, a beam intensity control and metering oir- Y the grid bias voltage may be adjusted, a second Y' ing a cathode anda beam intensity modulating i v .series and in.. series with the second voltageV cuit therefor comprising an adjustable source of source and the space current path. a capacitor grid, a beam intensity control and metering cir- -cuit therefor comprising an adjustable source of grid bias voltage connected to the cathode and t0 .the modulating grid, said bias voltage source compri g two rheostats mechanically ganged together, a resistor ,electrically connecting said two rheostats into a series-circuit, a direct current voltage source connected to said series circuit, circuits connecting said cathode and beam intensity grid to 'one oi said rheostats whereby voltage source, a vacuum tube repeater having a space current path, two resistors connected in assaasa modulating grid will be brought to, a,4 less negative voltage of magnitude predetermined bythe meter reading.

9. In an oscilloscope circuit oi the type employing a cathode and a beam intensitymodulating grid, a beam intensity control and metering circuit therefor comprising -an adjustable source of grid bias voltage connected to the cathode and to the modulating grid, said bias voltage source comprising ya rheostat, a resistor anda direct current voltage source connected in series, circuits connecting said cathode and beaml intensity grid to said rheostat whereby the grid bias voltage may be adjusted, a second voltage source, a vacuum tube repeater having a space current path, two resistors connected in series and in series with the secondvoltage source and the space current path, a capacitor shunting one of said two resistors, space current control means for the repeater, an input circuit for the repeater capable of blocking thev space current receiving a voltage pulse oi predetermined magnitude, a

cuit coupling the unshunted one of said two resistors to the modulating grid whereby upon sud-l denly Iblocking the space current said modulating grid will be brought to a less negative voltage of magnitude predetermined by the meter reading.

1l. In an oscilloscope circuit of the type employing acathode and a Ibeam intensityv modulating grid, a'beam intensity control and metering circult therefor comprising an adjustable source of grid bias voltage connected to the cathode and to the modulating grid, said Ibias voltage source comprising a, rheostat, a resistor and a direct current voltage source connected in series, y

circuits' connecting said cathodev and beam intensity grid to said rheostat whereby the grid the space current path, 'a capacitor shunting one of said two resistors, space current control means for the4 repeater, an input circuit for the repeater capable of blocking the space current upon receiving a voltage pulse of predetermined magnitude, al meter, a circuit connecting themeter with said bias adjusted means and said shunted resistor to cause the meter to indicate their difference voltage, and a circuit including `a series connected condenser coupling the unshunt- -ed one of said two resistors to the modulating grid whereby upon suddenly blocking the space meter, a circuit connecting the meter with said biasing adjusting meansv and said .'shunted resistor toy cause the meter to indicate their dif. ference voltage, and a circuit. coupling the urishunted one of said two resistors to the modulating grid whereby upon suddenly blocking the space current said modulating gridy will be brought to a less negative voltage oi' magnitudes predetermined lby the meter reading.

10. In an oscilloscope circuit of the type employing a cathode and a` beam intensity modulating grid, a beam intensity control and metering circuit therefor comprising an adjustable source of grid bias voltage connected to the cathode and to the modulating grid, said bias voltage source comprising a rheostat, a resistor and a direct cuxrent voltage source connected in se-- ries, circuits-connecting said cathode and beam intensity grid to said rheostat whereby the grid biasA voltage may be adjusted, a second voltage source,'a vacuum tube repeater having a space current path, two resistors ot equal resistance connected in series and in series with the secl ond voltage source and the space current path,

' a capacitor shunting one of said two resistors,

space current control means for the repeater, an

- input circuit for the repeater capable o! blocking current said modulating grid will be brought to a less negative voltage. of magnitude predetermined by the meter reading.

12. In an oscilloscope circuit of the type em ploying a cathode anda beam intensity modulating grid, a 'beam intensity control and metering cricuit. therefor comprising an adjustable source of grid bias voltage connected to the cathode and to the modulating grid, said bias voltage source comprising a rheostat, a'resistor and a direct current voltage source connected in series,

circuits connecting said cathode and [beam intensity grid to said rheostat whereby the grid .bias voltage may be adjusted, a second voltage source, a vacuum tube repeater having a space current path, two resistors connected in series and in series with the second voltage source and the space current path, a capacitor shunting one oi' said two resistors, space current control means for the repeater, an input circuit for the repeater including a series-connected diode capable of blocking the space current upon receiving a negative voltage `pulse of predetermined magnitude but rendering said space current insensitive to positive voltage pulses, a meter,v a vcircuit connecting the meter with said bias adjusting means and said shunted resistor to cause the meter t0 indicate their diierence voltage, and a circuit coupling the unshunted one of said two resistors to the modulating grid whereby upon suddenly .blocking the space current said modulating grid will be brought to a less negative voltage of masnitude predetermined by the meter reading.

JOHN J. MAHONEY, Jr. 

